French President Francois Hollande on Wednesday joined calls for international observers to oversee the evacuation of civilians trapped under fire in the wrecked city.

At a meeting with his defence cabinet, Hollande said those trapped by the fighting should "be evacuated in a dignified and safe manner, under the supervision of international observers and in the presence of humanitarian organizations," the presidency said in a statement.

Hollande also demanded that the population of eastern Aleppo receive "unconditional aid and protection" and said only a negotiated political transition could lead to "a lasting victory over terrorism" in Syria.

The French statement echoed a call by the US Ambassador to the UN Samantha Power, who said on Tuesday that foreign observers should be allowed in to "oversee the safe evacuation of the people who wish to leave but who justifiably fear that if they try, they will be shot in the street or carted off to one of (Syrian President Bashar al-) Assad's gulags."

On Wednesday, Aleppo was rocked anew by fierce clashes, jeopardizing a deal for the evacuation of civilians and fighters from remaining rebel-held areas.

French government spokesman Stephane Le Foll said France and Germany were pressing for the creation of humanitarian corridors allowing civilians out and aid agencies into the battered city.

He rejected calls for Hollande to take a leaf from late Socialist president Francois Mitterrand's book by visiting Aleppo.

"Saying all you need is for the president to visit Aleppo for everything to be resolved... is not responsible," he said.

Mitterrand flew into the besieged city of Sarajevo in 1992, braving shelling and sniper fire to show solidarity with hungry, terrorized civilians during the Bosnian War.